The invention is based on a fuel injection pump for internal combustion engines as defined hereinafter. Such so-called slide pumps are used primarily for high performance, that is, for use in trucks. With this kind of pump construction, the injection time adjusters needed for adhering to exhaust gas emission regulations and built into the pump drive mechanism, which however are limited in the work they can do, can be dispensed with. In the pump of this generic type, not only exact metering of the injection quantity but very accurate setting of the instant of injection onset can be attained by axially rotating the control slide and/or rotating the pump piston.
In these generic fuel injection pumps, there is inherently a relatively marked temperature development while driving, since because of the high injection pressures not only the mechanical production of heat, but also an overflow of the high-pressure fuel at the metering control edges can lead to heating of the returning fuel, which also heats the fuel located in the suction chamber. As the temperature varies, however, the physical properties such as density and compressibility vary as well, so that the quantity of fuel metered per pumping stroke, as well as its thermal energy content, varies with the temperature of the fuel delivered to the pump work chamber, so that during the ensuing injection, temperature differences in the delivered fuel result in altered performance in the engine cylinders. This effect is disadvantageously further reinforced by the fact that the actual heat sources between the pump piston and the control slide are remote from the actual heat dissipation locations between the pump piston and the pump cylinder, so that the known disadvantage of a lack of heat dissipation is made still worse.
In a known fuel injection pump of this type (German Offenlegungsschrift No. 21 46 578), the fuel is delivered at low pressure to the suction chamber by a feed pump, and from there it is fed via corresponding intake conduits to the pump work chamber during the intake stroke of the pump piston; then, as mentioned above, a portion of this fuel located in the pump work chamber is diverted at high pressure into the suction chamber during the compression stroke, in order to terminate injection supply. While the fuel temperature in the suction chamber near the entrance of the fuel inflow conduit is still relatively cool, because of the large proportion of fresh fuel, this temperature rises until it has attained its maximum in the area where the fuel leaves the suction chamber. The fuel temperatures in the individual pump work chambers of this injection pump differ correspondingly as well, with the consequences noted above. A further factor is that this temperature development also depends on the engine load; that is, at high load and high rpm, relatively little fuel is diverted, while in contrast a considerable quantity of fuel is diverted in the idling range. In any case, however, the ratio of the temperatures in the individual pump work chambers varies relative to one another, thus making it impossible to achieve an adaptation by the engine or some other system of the kind that is achievable when fixed values are involved. A uniform thermodynamic quality over the entire load and rpm range of the engine is attainable only if the fuel delivered to the individual pump work chambers has a largely uniform temperature.